With so much written about HTML5 video and canvas tags, but one of the other major additions to HTML5 has not been discussed at all: HTML5 audio. Firefox 4 has a cool new addition: the Audio Data API. You can us <audio id="audio" src="song.ogg"></audio> to embedd audio in to any webpages /blogs.
If you don't have Firefox 4 installed, or if you just want a quick overview of what you can expect from next generation of HTML5 Web apps, watch the video above. If you already have a nightly build of Firefox 4, play with the demos yourself! The 'beat detectors' require WebGL, which's easy enough to install.
More Info: HTML 5 Audio Data Demos